1. Field of the Invention
The invention provides a borosilicate glass having good solarization resistance, and for the use thereof for the production of glass tubes and the production of lamps, and for the use thereof in irradiation units, for example as top glass, a front pane or a shell tube. Solarization is understood to mean the decline in transparency for light of various wavelength ranges, which is caused by the action of short-wave ultraviolet (UV) radiation. In the broadest sense, the ultraviolet radiation range is understood to mean the wavelength range below that of visible light (about <380 namometers (nm)). In the narrower sense of this invention, the UV range is regarded as the wavelength range of about 100-330 nm.
2. Description of Related Art
Lamps, illuminants and irradiation units in general, which are exposed to ultraviolet radiation, require glasses with maximum solarization resistance. In order to be able to specify and establish the wavelength range and proportion of UV radiation transmitted and blocked, a defined position of the UV edge is also desired. The UV edge is understood to mean the transition in the transmission curve from the UV range of high transmission to the UV range of very low transmission down to the limit of transparency. Glasses of the type mentioned are required, for example, as top glass, or as a front pane or shell tube of irradiation devices, for example weathering systems. In such systems, for example, the ageing resistance of lacquers, pigments, materials, components and the like is studied. More particularly, they also serve to simulate the resistance of polymers to sunlight and to check the methods, guidelines or standards pertaining thereto.
In order to reduce any decline in transparency resulting from solarization effects during the use of glasses, it is known that glasses can be pre-aged by UV irradiation. However, this method is inconvenient and associated with corresponding costs, and leads to an unsatisfactory result for many applications, since the pre-aged glasses have a low transmission overall. There is therefore still a need for more solarization-resistant glasses.
The applicant supplies, for example, a borosilicate glass of the 8281 type for UV filters, which suppresses the transmission of particular UV components through its preset position of the UV edge, while visible light and near infrared is transmitted in high proportions. As an essential component which influences UV radiation, this glass receives blocking with molybdenum oxide MoO3.
DE 10 2008 043 317 A likewise describes a glass wherein the UV blocking is established particularly by an MoO3 content. To influence the transmission properties, especially in the short-wave range, additional assisting contents of TiO2 and Bi2O3 are proposed.
For particular applications, however, the distribution of the short-wave light transmitted is unsuitable, or the solarization resistance is inadequate.